A continuation of preliminary studies on human gastric K ion activity, H ion transportation ATPase are proposed involving: a) further purification of the ATPase, b) characterization of the enzymatic and transport pathways, i.e., H ion and K ion transport, c) characterization of the various phosphorylated intermediates of the ATPase reaction, d) immunological localization and antibody effect on H ion secretion, e) identification of primary energy source for H ion secretion.